Double eccentric valve

ABSTRACT

A double eccentric valve includes a first bearing and a second bearing spaced apart from each other along a center axis of a rotary shaft. When a motor is operated and the valve element is at a controlled folly-closed position corresponding to a fully-closed state, the rotary shaft is inclined about the first bearing serving as a fulcrum and is out of contact with the second bearing. When a valve opening degree is a predetermined opening degree corresponding to a valve open state of the valve element, the rotary shaft is restrained by the second bearing. In a small opening range between the valve opening degree at the controlled fully-closed position and the predetermined small opening degree, a variation amount in open area relative to a variation amount in valve opening degree is smaller than that in an opening range larger than the predetermined opening degree.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.15/301,777, filed on Oct. 4, 2016, which is the US national stage ofInternational Application No. PCT/JP2015/068197, filed on Jun. 24, 2015,which claims priority of Japanese patent application No. 2014-134268,filed on Jun. 30, 2014, the entire contents and disclosures of which arehereby incorporated by reference in their entireties and for ailpurposes.

BACKGROUND Technical Field

This disclosure relates to a double eccentric or offset valve in which avalve element is placed with a rotation center (a rotary shaft)positioned eccentrically from a center of a valve hole of a valve seatand a sealing surface of the valve element is positioned eccentricallyfrom the rotary shaft.

Related Art

Patent Document 1 discloses an exhaust gas recirculation apparatusconfigured to open a valve element of a butterfly valve from afully-closed position and stop at a predetermined opening degree,thereby preventing sticking between a valve seat and a valve element dueto deposits during non-energization of a rotary solenoid.

RELATED ART DOCUMENTS Patent Documents

Patent Document 1: JP-A-2001-214816

SUMMARY Technical Problems

However, the technique disclosed in Patent Document 1 fails to disclosevariations in flow rate in a small opening range.

The present disclosure has been made in view of the circumstances tosolve the above problems and has a purpose to provide a double eccentricvalve capable of reducing variations in flow rate in a small openingrange to a minimum.

Means of Solving the Problems

To achieve the above purpose, one aspect of the disclosure provides adouble eccentric valve comprising: a valve seat including a valve holeand a seat surface formed at an edge of the valve hole; a valve elementformed with a sealing surface on an outer periphery corresponding to theseat surface; a rotary shaft integrally provided with the valve elementto rotate the valve element, the rotary shaft having a central axisextending in parallel to a radial direction of the valve element and thevalve hole, the central axis of the rotary shaft being positionedeccentrically from a center of the valve hole in another radialdirection of the valve hole, and the sealing surface being positionedeccentrically from the central axis of the rotary shaft toward anextending direction of a central axis of the valve element, wherein thedouble eccentric valve further comprises: a drive mechanism configuredto generate a drive force to rotate the rotary shaft in a valve openingdirection; a drive force receiving part integrally provided with therotary shaft and configured to receive the drive force; and a bearingplaced in a position between the valve element and the drive forcereceiving part in a direction of the central axis of the rotary shaft tosupport the rotary shaft, the bearing includes a first bearing and asecond bearing spaced apart from each other along a central axis of therotary shaft, when the drive mechanism is operated and the valve elementis at a controlled fully-closed position corresponding to a fully-closedstate of the valve element, the rotary shaft is inclined about the firstbearing serving as a fulcrum and the rotary shaft is out of contact withthe second bearing, when a valve opening degree of the rotary shaft is apredetermined small opening degree corresponding to a valve open stateof the valve element, the rotary shaft is restrained by the secondbearing from further inclining, and in a small opening range between thevalve opening degree when the valve element is at the controlledfully-closed position and the predetermined small opening degree, anamount of variation in an open area formed between the valve element andthe valve seat relative to an amount of variation in the valve openingdegree is smaller than that in an opening range larger than thepredetermined small opening degree.

According to the above aspect, variations in flow rate in a smallopening range can be reduced to a minimum.

Effects of the Disclosure

A double eccentric valve of the present disclosure can reduce variationsin flow rate in a small opening range to a minimum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an electrically-operated EGR valve providedwith a double eccentric valve;

FIG. 2 is a top view of the electrically-operated EGR valve providedwith the double eccentric valve;

FIG. 3 is a partially-cutaway perspective view of a valve unit in afully-closed state where a valve element is seated on a valve seat;

FIG. 4 is a partially-cutaway perspective view of the valve unit in afully-open state where the valve element is separated furthest from thevalve seat;

FIG. 5 is a side view of the valve seat, the valve element, and a rotaryshaft in the fully-closed state;

FIG. 6 is a cross-sectional view taken along a line A-A in FIG. 5;

FIG. 7 is a cross-sectional view taken along a line B-B in FIG. 1;

FIG. 8 is a cross-sectional view taken along a line C-C in FIG. 1;

FIG. 9 is a front view showing a state where an end frame has beendetached from a valve housing;

FIG. 10 is an enlarged view (a partially-cutaway view) of a main gear, areturn spring, and an intermediate gear during non-operation of a motor;

FIG. 11 is a schematic view showing forces acting on the main gearduring non-operation of the motor and seen from a main gear side in acentral axis direction of a rotary shaft;

FIG. 12 is a schematic view representing the valve seat, the valveelement, the rotary shaft, bearings, and the main gear, showing across-sectional view taken along a line D-D in FIG. 11;

FIG. 13 is a schematic view showing forces acting on the main gearduring operation of the motor and seen from the main gear side in thecentral axis direction of the rotary shaft;

FIG. 14 is a schematic view representing the valve seat, the valveelement, the rotary shaft, the bearings, and the main gear, showing across-sectional view taken along a line E-E in FIG. 13;

FIG. 15 is a diagram corresponding to FIG. 14, and representing a casewhere a motor drive force is set larger than that in FIG. 14;

FIG. 16 is an enlarged view (a partially-cutaway view) of the main gear,the return spring, the intermediate gear, and their surrounding parts ata valve opening degree of a during operation of the motor;

FIG. 17 is a diagram corresponding to FIG. 15, and representing a casewhere a motor drive force is set larger than that in FIG. 15;

FIG. 18 is an enlarged view (a partially-cutaway view) of the main gear,the return spring, the intermediate gear, and their surrounding parts ata valve opening degree of β during operation of the motor;

FIG. 19 is a graph showing a relationship between valve opening degreeand open area;

FIG. 20 is a schematic view of a valve seat, a valve element, a rotaryshaft, bearings, and main gear in a modified example; and

FIG. 21 is a graph showing a relationship between valve opening degreeand open area in the modified example.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

As shown in FIGS. 1 and 2, an EGR valve 1 includes a valve unit 2,constituted of a double eccentric valve, and a drive mechanism unit 3.The valve unit 2 includes a pipe part 12 (see FIG. 7) formed with a flowpassage 11 allowing EGR gas as a fluid to flow therethrough. In thisflow passage 11, a valve seat 13, a valve element 14, and a rotary shaft15 (see FIGS. 7 and 8) are arranged. The rotary shaft 15 receives driveforce (torque) from the drive mechanism unit 3. This drive mechanismunit 3 is provided with a motor 32 and a speed reducing mechanism 33(see FIG. 7).

As shown in FIGS. 3 and 4, the flow passage 11 is formed with a steppedportion 10 in which the valve seat 13 is fixed by press fit. The valveseat 13 has an annular shape formed with a valve hole 16 in the center.On an edge of the valve hole 16, an annular seat surface 17 is formed.The valve element 14 has a circular disc shape with an annular sealingsurface 18 on an outer periphery corresponding to the seat surface 17.The valve element 14 is fixed to the rotary shaft 15 and movableintegrally with the rotary shaft 15. In FIGS. 3 and 4, the flow passage11 below the valve element 14 represents an upstream side in the flow ofEGR gas, while the flow passage 11 above the valve seat 13 represents adownstream side in the flow of EGR gas. In the flow passage 11,specifically, the valve element 14 is fixed on a more upstream side in aflow direction of EGR gas than the valve seat 13.

As shown in FIGS. 5 and 6, the central axis Ls of the rotary shaft 15extends in parallel to a radial direction of the valve element 14 andthe valve hole 16 and is placed eccentrically, or offset, from thecenter P1 of the valve hole 16 in another radial direction of the valvehole 16. The sealing surface 18 of the valve element 14 is placedeccentrically toward an extending direction of the central axis Lv ofthe valve element 14 from the central axis Ls of the rotary shaft 15.The valve element 14 is configured to rotate about the central axis Lsof the rotary shaft 15 between a fully closed position (a controlledfully-closed position) in which the sealing surface 18 of the valveelement 14 is in surface contact with the seat surface 17 of the valveseat 13 (see FIG. 3) and a fully open position (see FIG. 4) in which thesealing surface 18 is furthest away from the seat surface 17.

As shown in FIGS. 7 and 8, a valve housing 35 made of metal or syntheticresin is provided with the flow passage 11 and the pipe part 12. An endframe 36 made of metal or synthetic resin closes an open end of thevalve housing 35. The valve element 14 and the rotary shaft 15 areprovided in the valve housing 35. The rotary shaft 15 includes a pin 15a protruding from a distal end of the rotary shaft 15. Specifically, thepin 15 a is provided at one end of the rotary shaft 15 (on a side closeto the valve element 14) in a direction of the central axis Ls (see FIG.8). At the other end of the rotary shaft 15 (on a side close to the maingear 41) in the direction of the central axis Ls, there is provided aproximal end portion 15 b.

The rotary shaft 15 has a free end on a distal end side provided withthe pin 15 a, so that the distal end is inserted and placed in the flowpassage 11 of the pipe part 12. The rotary shaft 15 is supported by acantilever structure with a first bearing 37 and a second bearing 38 andin rotatable manner with respect to the valve housing 35 through thefirst bearing 37 and the second bearing 38 spaced from each other. Thefirst bearing 37 and the bearing 38 are each constituted of a ballbearing. The first bearing 37 and the second bearing 38 are placed inrespective positions between the valve element 14 and the main gear 41along the central axis Ls of the rotary shaft 15 to rotatably supportthe rotary shaft 15. The valve element 14 is fixed by welding to the pin15 a formed at the distal end of the rotary shaft 15 and is placed inthe fixed flow passage 11.

The end frame 36 is fixed to the valve housing 35 with a plurality ofclips 39 (see FIGS. 1 and 2). As shown in FIGS. 7 and 8, to the proximalend portion 15 b of the rotary shaft 15, a main gear 41 provided with afan-shaped gear is fixed. There is a provided a return spring 40 betweenthe valve housing 35 and the main gear 41 to generate return springforce Fs1 (see FIG. 11). The return spring force Fs1 is a force torotate the rotary shaft 15 in a valve closing direction and also a forceto urge the valve element 14 in the valve closing direction.

The return spring 40 is an elastic member made of wire wound in a coilshape and is provided, at both ends, with a far-side hook 40 a and anear-side hook 40 b. As shown in FIG. 10, the far-side hook 40 a and thenear-side hook 40 b are spaced apart from each other at an interval ofabout 180° in a circumferential direction of the return spring 40. Thefar-side hook 40 a is located on a valve housing 35 side (on a far-sideof a drawing sheet of FIG. 10) so that it contacts a spring hook part 35c (see FIG. 18) of the valve housing 35. In contrast, the near-side hook40 b is located on a main gear 41 side (on a near-side of the drawingsheet of FIG. 10) so that it contacts a spring hook part 41 c of themain gear 41.

As shown in FIGS. 7 to 10, the main gear 41 includes a full-closestopper part 41 a, a gear part 41 b, the spring hook part 41 c, a springguide part 41 d, and others. In the circumferential direction (acounterclockwise direction in FIG. 10) of the main gear 41, thefull-close stopper part 41 a, the gear part 41 b, and the spring hookpart 41 c are arranged in this order. The main gear 41 is integrallyprovided with the rotary shaft 15 and is configured to receive driveforce generated by the motor 32. The full-close stopper part 41 a is apart that abuts on the foil-close stopper part 35 b of the valve housing35 when a valve opening degree θ is 0.

The valve opening degree θ is a rotation angle of the rotary shaft 15rotated about the central axis Ls and corresponds to a rotation angle ofthe main gear 41, an opening angle of the valve element 14, or anopening degree of the EGR valve. In other words, the time when the valveopening degree θ is 0 represents the time when the rotation angle of therotary shaft 15 is a minimum angle within a rotatable range of therotary shaft 15. FIGS. 7 to 10 show the time when the valve openingdegree θ is 0.

As shown in FIG. 10, the gear part 41 b meshes with a small-diametergear 42 b of an intermediate gear 42. The spring hook part 41 c contactswith the near-side hook 40 b of the return spring 40 and receives thereturn spring force Fs1 from the near-side hook 40 b (see FIG. 11).

As shown, in FIG. 8, the spring guide part 41 d is placed in the coiledreturn spring 40 to support the return spring 40. The spring guide part41 d is integrally provided, at a portion located close to a proximalend 15 b of the rotary shaft 15, with the rotary shaft 15.

The main gear 41 includes a recess 41 e in which a magnet 46 having asubstantially disk shape is mounted as shown in FIG. 8. Therefore, whenthe main gear 41 rotates together with the valve element 14 and therotary shaft 15, the magnet 46 is also rotated, changing a magneticfield of the magnet 46. This change in the magnetic field of the magnet46 is detected by a rotation angle sensor (not illustrated), so that therotation angle of the main gear 41 is detected as the opening degree ofthe valve element 14, that is, the opening degree of the EGR valve.

As shown in FIG. 7, the motor 32 is accommodated and fixed in a holdingcavity 35 a formed in the valve housing 35. The motor 32 is drivinglycoupled to the rotary shaft 15 through the speed reducing mechanism 33to operate the valve element 14 to open and close. Specifically, anoutput shaft 32 a (see FIG. 9) of the motor 32 is fixedly provided witha motor gear 43. This motor gear 43 is drivingly coupled to the maingear 41 through the intermediate gear 42. The motor 32 generates driveforce to rotate the rotary shaft 15 in a valve opening direction and ina valve closing direction.

The intermediate gear 42 is a double gear having a large-diameter gear42 a and the small-diameter gear 42 b and is rotatably supported by thevalve housing 35 through a pin shaft 44. The large-diameter gear 42 a isdrivingly engaged with the motor gear 43, while the small-diameter gear42 b is drivingly engaged with the main gear 41. In the presentembodiment, each of the gears 41 to 43 constituting the speed reducingmechanism 33 is a plastic gear made of resin material for weight saving.

The motor 32 is one example of a “drive mechanism” in the presentdisclosure. Further, the intermediate gear 42 transmits the drive forceof the motor 32 to the rotary shaft 15 and corresponds to one example ofa “drive transmission part” in the present disclosure.

In the EGR valve 1 configured as above, when the motor 32 is energizedfrom a state where the valve element 14 is in a fully closed position asshown in FIG. 3, the force pushing the gear teeth (the motor drive forceFm1 (see FIG. 13)) is exerted on the main gear 41, thereby moving therotary shaft 15 (the valve element 14) in a direction toward the valveseat 13 by the principle of leverage. Thereafter, when the drive voltage(current) applied to the motor 32 is gradually raised, the output shaft32 a and the motor gear 43 are rotated in a forward direction (i.e., adirection to open the valve element 14) and this rotation is reduced inspeed and then transmitted to the main gear 41. Accordingly, the valveelement 14 is opened against the return spring force Fs1 that isgenerated by the return spring 40 and that urges the valve element 14 inthe valve closing direction. The flow passage 11 is thus opened.Thereafter, when the drive voltage applied to the motor 32 is maintainedat a constant level in the process of opening the valve element 14, themotor drive force Fm1 and the return spring force Fs1 become balancedwith each other at the opening degree of the valve element 14 at thattime, so that the valve element 14 is held at a predetermined openingdegree.

More details of the operations of the EGR valve 1 in the presentembodiment will be described below. During non-operation of the motor 32that is not energized (i.e., during the time when the motor 32 isstopped), the valve opening degree θ is 0 (the rotary shaft 15 is in thevalve-closed state). At that time, as shown in FIG. 10, the full-closestopper part 41 a of the main gear 41 contacts with the full-closestopper part 35 b of the valve housing 35. During that period, theengine is stopped.

The relationship of forces in terms of a circumferential direction of,or around, the rotary shaft 15 during the non-operation of the motor 32is considered as below. The spring hook part 41 c of the main gear 41receives the return spring force Fs1 from the near-side hook 40 b of thereturn spring 40 as shown in FIG. 11. As shown in FIG. 11, in arectangular or Cartesian coordinate system consisting of an originrepresented by the central axis Ls of the rotary shaft 15, an x-axisrepresented by a horizontal line, and a y-axis represented by a verticalline, a first quadrant is a part defined by a +x axis and a +y axis, asecond quadrant is a part defined by a −x axis and the +y axis, a thirdquadrant is a part defined by the −x axis and a −y axis, and a fourthquadrant is a part defined by the +x axis and the −y axis. During thenon-operation of the motor 32, the far-side hook 40 a and the full-closestopper part 41 a are placed in a position corresponding to the firstquadrant, and the near-side hook 40 b and the spring hook part 41 c areplaced in a position corresponding to the third quadrant.

The relationship of forces in terms of a cross section of the rotaryshaft 15 taken along the central axis Ls is also considered as below. A+y direction component force of the return spring force Fs1 acts on themain gear 41 (in an arrow direction as shown in FIG. 12). The +ydirection represents a direction perpendicular to the central axis Ljdirection of the first bearing 37 and the second bearing 38 (the xdirection) and a direction toward which the valve seat 13 is placedrelative to the valve element 14 (an upward direction in the drawingsheets of FIGS. 11 and 12).

When the +y direction component force of the return spring force Fs1acts on the main gear 41, the rotary shaft 15 integral with the maingear 41 is caused to turn and incline clockwise in FIG. 12 about thefirst bearing 37 serving as the fulcrum. Accordingly, by the principleof leverage, the main gear 41 provided in the proximal end 15 b of therotary shaft 15 is moved in the +y direction, while the valve element 14provided in the pin 15 a of the rotary shaft 15 is moved in the −ydirection. Therefore, the valve element 14 is moved m a direction awayfrom the valve seat 13 (a separating direction). Further, at that time,the rotary shaft 15 is restrained by the second bearing 38 from fartherinclining. Thus, the valve element 14 is stopped at a position separatedby a slight distance from the valve seat 13. In the above manner, duringthe time when the motor 32 is not operated and the rotary shaft 15 is inthe valve closed state, a slight gap is generated between the valve seat13 and the valve element 14. The valve element 14 at that time islocated at a position represented by a point P1 a in FIG. 19 showing arelationship between the valve opening degree θ and the open area S.Herein, the time when the rotary shaft 15 is in the valve closed statecorresponds to the time when the valve opening degree θ (the openingdegree of the valve element 14) is 0, that is, the time when therotation angle of the rotary shaft 15 is an angle during valve closing(the minimum angle within the rotatable angle of the rotary shaft 15).

Thereafter, during operation of the motor 32, namely, when the motor 32is energized, the motor drive force Fm1 acts from the small-diametergear 42 b (see FIG. 10) of the intermediate gear 42 to the gear part 41b (see FIG. 10) of the main gear 41 to rotate the main gear 41. Whenseen from the force relationship in terms of the circumferentialdirection of the rotary shaft 15 at that time, the motor drive force Fm1acts in the −y direction as shown in FIG. 13. This −y direction is aperpendicular direction to the central axis Lj direction (the xdirection) of the first bearing 37 and the second bearing 38 and adirection toward which the valve element 14 is placed relative to thevalve seat 13 (a downward direction in the drawing sheets of FIGS. 13and 14).

As shown in FIG. 14, when the motor drive force Fm1 that acts on themain gear 41 in the −y direction becomes larger than the +y directioncomponent force of the return spring force Fs1, the rotary shaft 15integral with the main gear 41 is caused to turn and inclinecounterclockwise in FIG. 14 about the first bearing 37 serving as thefulcrum. Accordingly, by the principle of leverage, the main gear 41 ismoved in the −y direction, while the valve element 14 moves in the +ydirection. Therefore, the valve element 14 is moved in a directiontoward the valve seat 13 (a seating direction) by the motor drive forceFm1. In the present embodiment, the valve element 14 gets seated on thevalve seat 13. The valve element 14 at that time is located at aposition represented by a point P1 b in FIG. 19 showing the relationshipbetween the valve opening degree θ and the open area S. At that time,when an engine (not illustrated) is being driven, the valve element 14is assisted by differential pressure Fb between an upstream side and adownstream side of the valve element 14.

Thereafter, when the drive voltage to be applied to the motor 32 risesand thus the motor drive force Fm1 become large, the rotary shaft 15 iscaused to further turn and incline counterclockwise in FIG. 15 about thefirst bearing 37 serving as the fulcrum. Accordingly, the main gear 41is further moved in the −y direction, while the valve element 14 isfurther moved in the +y direction. Thus, the valve element 14 is furthermoved in the direction toward the valve seat 13, and the rotary shaft 15is restrained by the second bearing 38 from further inclining. At thattime, the rotary shaft 15 is rotated about the central axis Ls while thevalve element 14 remains seated on the valve seat 13, so that the valveopening degree θ (the rotation angle of the rotary shaft 15) becomes “α”(see FIG. 16) and the open area S increases. In this state, thefull-close stopper part 41 a of the main gear 41 separates from thefoil-close stopper part 35 b of the valve housing 35 as shown in FIG.16. The valve element 14 at that time is located at a positionrepresented by a point P1 c in FIG. 19 showing the relationship betweenthe valve opening degree θ and the open area S.

Thereafter, as the motor drive force Fm1 becomes larger, the rotaryshaft 15 is further rotated about the central axis Ls. This causes thevalve element 14 to separate from the valve seat 13 as shown in FIG. 17,further increasing the open area S. At that time, the valve openingdegree θ becomes “β” (see FIG. 18). The valve element 14 at that time islocated at a position represented by a point P1 d in FIG. 19 showing therelationship between the valve opening degree θ and the open area S. Inthe above manner, the valve opening operation of the EGR valve 1 isperformed by the motor drive force Fm1.

In the present embodiment, the EGR valve 1 includes the two, first andsecond, bearings 37 and 38. Instead of these first and second bearings37 and 38, a single bearing may be installed or three or more bearingsmay be installed.

The EGR valve 1 configured as above in the present embodiment generatesthe the +y direction component force of the return spring force Fs1during non-operation of the motor 32. This +y direction component forceof the return spring force Fs1 is a force that is caused by the returnspring force Fs1 and that acts in a perpendicular direction to thecentral axis Lj of the first bearing 37. The +y direction componentforce of the return spring force Fs1 causes the rotary shaft 15 to turnand incline about the first bearing 37 serving as the fulcrum, therebybiasing the valve element 14 in the direction away from the valve seat13.

Accordingly, when the EGR valve 1 is in the valve closed state duringengine stop and non-operation of the motor 32, a slight gap is generatedbetween the valve seat 13 and the valve element 14. Thus, even whendeposits adhere to the valve seat 13 or the valve element 14, the valveseat 13 and the valve element 14 are prevented from sticking to eachother. Further, sticking between the valve seat 13 and the valve element14 due to freezing is also prevented. This can achieve stable openingand closing operations of the EGR valve 1. Since the valve element 14 ismoved in the direction away from the valve seat 13, in case foreignmatters are caught between the valve seat 13 and the valve element 14during the valve closing operation, the foreign, matters are allowed tofall away. Thus, no biting occurs between the valve seat 13 and thevalve element 14. Consequently, sticking between the valve seat 13 andthe valve element 14 can be prevented reliably.

According to the present embodiment, moreover, there is no need toprovide special components (e.g., a spring) for separating the valveelement 14 from the valve seat 13 in addition to the return spring 40.This can achieve reduced cost.

In the present embodiment, only the return spring force Fs1 acts duringnon-operation of the motor 32. Thus, even when the rotary shaft 15 iscaused to turn and incline about the first bearing 37 serving as thefulcrum, only a small force acts on the first bearing 37. The firstbearing 37 is therefore less damaged.

In the present embodiment, to be specific, the +y direction componentforce of the return spring force Fs1 is generated when the motor 32 isnot operated and the rotary shaft 15 is in the valve closed state.Herein, the time “when the rotary shaft 15 is in the valve closed state”corresponds to the time when the valve opening degree θ is 0.

In the present embodiment, the motor drive force Fm1 is generated whenthe motor 32 is operated. This motor drive force Fm1 is the force thatacts in the direction perpendicular to the central axis Lj of the firstbearing 37. The motor drive force Fm1 causes the rotary shaft 15 to turnand incline about the first bearing 37 serving as the fulcrum, therebybiasing the valve element 14 in the direction toward the valve seat 13.

Accordingly, the open area S (the gap between the valve seat 13 and thevalve element 14) at the initial stage of the valve opening operation isdecreased. This can reduce a flow rate when the opening degree of thevalve element 14 is small (when the valve opening degree θ is small).Thus, the accuracy of flow control with the valve element 14 at a smallopening degree can be enhanced.

In the present embodiment, the valve element 14 is seated on the valveseat 13 by the motor drive force Fm1. To be specific, the EGR valve 1operates to seat the valve element 14 once on the valve seat 13 by themotor drive force Fm1 and then open the valve element 14.

Thus, the open area S at the initial stage of valve opening can befurther decreased. Accordingly, the flow rate when the valve element 14is at a small opening degree can be further decreased. The accuracy ofthe flow control with the valve element 14 at the small opening degreecan be further enhanced.

In the present embodiment, the EGR valve 1 may be configured to controlthe opening degree of the valve element 14 relative to a referenceposition determined by an opening degree of the valve element 14positioned to allow fluid to flow at a predetermined flow rate. In theEGR valve L for instance, the flow control is performed by controllingthe valve opening degree θ relative to a (see FIG. 19). A control unit50 (see FIG. 1) for performing this control is installed in the EGRvalve 1 or provided separately from the EGR valve 1. Accordingly,variations in flow rate at the reference position for the flow controlare reduced, resulting in enhanced accuracy of the flow rate withrespect to the valve opening degree θ.

Further, the EGR valve 1 may be configured to control the opening degreeof the valve element 14 relative to the reference position determined byan opening degree of the valve element 14 positioned in the valve closedstate. In the EGR valve 1, for example, the flow control is performed bycontrolling the valve opening degree θ with reference to 0. The controlunit 50 for performing this control is installed in the EGR valve 1 orprovided separately from the EGR valve 1. Accordingly, the referenceposition for the flow control is unambiguously determined, resulting inenhanced accuracy of the flow rate with respect to the valve openingdegree θ.

Further, the EGR valve 1 includes the intermediate gear 42 placedbetween the motor 32 and the main gear 41. The intermediate gear 42transmits the drive force of the motor 32 from the motor 32 to the maingear 41.

Accordingly, the drive force from the motor 32 is increased by theintermediate gear 42 and such an increased drive force is transmitted tothe main gear 41. Therefore, the drive force to be generated by themotor 32 can be reduced, resulting in downsizing of the motor 32.

The following modified example is also adoptable. In this modifiedexample, as shown in FIG. 20, in the EGR valve 1 in the valve closedstate (the valve opening degree θ is 0), even when the valve element 14is urged toward the valve seat 13 by the motor drive force Fm1, thevalve element 14 does not seat on the valve seat 13. Thus, the open areaS is slightly generated. The valve element 14 at that time is located ata position represented by a point P2 b in FIG. 21 showing therelationship between the valve opening degree θ and the open area S.

As above, when the valve element 14 is urged in a direction toward thevalve seat 13 by the motor drive force Fm1, the open area S is slightlygenerated. Thus, the valve seat 13 and the valve element 14 areprevented from rubbing against each other during the valve openingoperation.

Thereafter, when the motor drive force Fm1 is further increased, therotary shaft 15 is rotated, increasing the valve opening degree θ andthe open area S as shown in FIG. 21. The valve element 14 at that timeis located at a position represented by a point P2 c in FIG. 21 showingthe relationship between the valve opening degree θ and the open area S.

The aforementioned embodiments are mere examples and do not give anylimitations to the present disclosure. Thus, various improvements andmodifications may be available in a scope without departing from theessential characteristics thereof. For instance, the rotary shaft 15 maybe supported by a both-ends-supported structure with the first bearing37 and a bearing (not illustrated) separately provided on the oppositeside of the valve element 14 from the first bearing 37.

Moreover, in the technique disclosed in Patent Document 1, the butterflyvalve stops at a certain position within a rotatable range of thebutterfly valve. Thus, if the gap between the valve seat and the valveelement is made small to reduce a leakage amount, for example, bitingmay occur between the valve seat and the valve element. Therefore,sticking between the valve seat and the valve element could not beprevented reliably.

Therefore, one aspect of the disclosure provides a double eccentricvalve comprising: a valve seat including a valve hole and a seat surfaceformed at an edge of the valve hole; a valve element formed with asealing surface on an outer periphery corresponding to the seat surface;a rotary shaft integrally provided with the valve element to rotate thevalve element, the rotary shaft having a central axis extending inparallel to a radial direction of the valve element and the valve hole,the central axis of the rotary shaft being positioned eccentrically froma center of the valve hole in another radial direction of the valvehole, and the sealing surface being positioned eccentrically from thecentral axis of the rotary shaft toward an extending direction of acentral axis of the valve element, wherein the double eccentric valvefurther comprises: a drive mechanism configured to generate a driveforce to rotate the rotary shaft in a valve opening direction; a driveforce receiving part integrally provided with the rotary shaft andconfigured to receive the drive force; a bearing placed in a positionbetween the valve element and the drive force receiving part in adirection of the central axis of the rotary shaft to support the rotaryshaft; and a return spring configured to generate a return spring forceto rotate the rotary shaft in a valve closing direction, and wherein,during non-operation of the drive mechanism, the double eccentric valvegenerates a separating-direction urging force to cause the rotary shaftto incline about the bearing serving as a fulcrum and urge the valveelement in a direction away from the valve seat, theseparating-direction urging force being a force caused by the returnspring force and acting in a direction perpendicular to a central axisof the bearing.

According to the above aspect, when the double eccentric valve is in avalve-closed state during engine stop and non-operation of a drivemechanism, a slight gap is generated between the valve seat and thevalve element. Therefore, even when deposits adhere to the valve seat orthe valve element, the valve seat and the valve element can be preventedfrom sticking to each other. Further, the valve seat and the valveelement can also be prevented from sticking to each other due tofreezing. Accordingly, the double eccentric valve can perform stableopening and closing operations. Further, the valve element is moved in adirection away from the valve seat by the separating-direction urgingforce. Even if foreign matters are caught between the valve seat and thevalve element during valve closing operation, the foreign matters do notdrop off and thus do not cause biting between the valve seat and thevalve element. This can reliably prevent the valve seat and the valveelement from sticking to each other.

In the above aspect, preferably, during operation of the drivemechanism, the double eccentric valve generates a seating-directionurging force to cause the rotary shaft to incline the rotary shaft aboutthe bearing serving as the fulcrum and urge the valve element in adirection toward the valve seat, the seating-direction urging forcebeing a force caused by the drive force and acting in a directionperpendicular to the central axis of the bearing.

According to the above aspect, the open area (the gap between the valveseat and the valve element) at an initial stage of a valve openingoperation can be set small. Thus, a low flow rate can be achieved by thevalve element at a small opening degree. This can enhance the accuracyof flow control while the valve element is at the small opening degree.

In the above aspect, preferably, the valve element is caused to seat onthe valve seat by the seating-direction urging force.

According to the above aspect, the open area at the initial stage of thevalve opening operation can be set smaller than the above case. Thus, alower flow rate can be achieved by the valve element at the smallopening degree. This can enhance the accuracy of flow control while thevalve element is at the small opening degree.

In the above aspect, preferably, the double eccentric valve isconfigured to control an opening degree of the valve element relative toa reference position determined by an opening degree of the valveelement positioned to allow fluid to flow at a predetermined flow rate.

According to the above aspect, variations in the flow rate in thereference position of the flow control is reduced, so that the accuracyof flow rate with respect to the opening degree of the valve element canbe enhanced.

In the above aspect, preferably, the double eccentric valve isconfigured to control an opening degree of the valve element relative toa reference position determined by an opening degree of the valveelement positioned in a valve closed state.

According to the above aspect, the reference position of the flowcontrol is uniquely determined, so that the accuracy of flow rate withrespect to the opening degree of the valve element can be enhanced.

The above aspect, preferably, further comprises a drive transmissionpart placed between the drive mechanism and the drive force receivingpart and configured to transmit the drive force from the drive mechanismto the drive force receiving part.

According to the above aspect, the drive transmission part can increaseand transmit the drive force received from the drive mechanism. Thus,the drive force to be generated by the drive mechanism can be set small.This can reduce the size of the drive mechanism.

REFERENCE SIGNS LIST

-   1 EGR valve-   2 Valve unit-   3 Drive mechanism-   11 Flow passage-   13 Valve seat-   14 Valve element-   15 Rotary shaft-   15 a Pin-   15 b Proximal end-   16 Valve hole-   17 Seat surface-   18 Sealing surface-   32 Motor-   32 Speed reducing mechanism-   35 Valve housing-   35 b Full-close stopper part-   35 c Spring hook part-   37 First bearing-   38 Second bearing-   40 Return spring-   40 a Far-side hook-   40 b Near-side hook-   41 Main gear-   41 a Full-close stopper part-   41 b Gear part-   41 c Spring hook part-   41 d Spring guide part-   Ls Central axis (of rotary shaft)-   Lv Central axis (of valve element)-   Lj Central axis (of bearing)-   Fs1 Return spring force-   Fm1 Motor drive force-   θ Valve opening degree

What is claimed is:
 1. A double eccentric valve comprising: a valve seatincluding a valve hole and a seat surface formed at an edge of the valvehole; a valve element formed with a sealing surface on an outerperiphery corresponding to the seat surface; a rotary shaft integrallyprovided with the valve element, to rotate the valve element, the rotaryshaft having a central axis extending in parallel to a radial directionof the valve element and the valve hole, the central axis of the rotaryshaft being positioned eccentrically from a center of the valve hole inanother radial direction of the valve hole, and the sealing surfacebeing positioned eccentrically from the central axis of the rotary shafttoward an extending direction of a central axis of the valve element,wherein the double eccentric valve further comprises: a drive mechanismconfigured to generate a drive force to rotate the rotary shaft in avalve opening direction; a drive force receiving part integrallyprovided with the rotary shaft and configured to receive the driveforce; and a bearing placed in a position between the valve element andthe drive force receiving part in a direction of the central axis of therotary shaft to support the rotary shaft, the bearing includes a firstbearing and a second bearing spaced apart from each other along acentral axis of the rotary shaft, when the drive mechanism is operatedand the valve element is at a controlled fully-closed positioncorresponding to a fully-closed state of the valve element, the rotaryshaft is inclined about the first bearing serving as a fulcrum and therotary shaft is out of contact with the second bearing, when a valveopening degree of the rotary shaft is a predetermined small openingdegree corresponding to a valve open state of the valve element, therotary shaft is restrained by the second bearing from further inclining,and in a small opening range between the valve opening degree when thevalve element is at the controlled fully-closed position and thepredetermined small opening degree, an amount of variation in an openarea formed between the valve element and the valve seat relative to anamount of variation in the valve opening degree is smaller than that inan opening range larger than the predetermined small opening degree.